My mom has floated it as an option for her to more cheaply and easily get to the Adirondacks via United (JetBlue/Cape Air from BWI via BOS is pricey). For me, it seems like a reasonable alternative to driving to Dulles (or taking a super-pricey Lyft) on those rare occasions I can only fly out of Dulles. Has anybody here used it?

the other option is tale MARC to metro then to end of silver then shuttle bus to IAD. From BWI it will be about $7 MARc+ metro fare from Union to Reston+ $6 for Reston to Dulles.

To clarify, BWI is only the starting point because it makes sense to get a rideshare to there from north of Baltimore to catch that shuttle. So it would otherwise be MARC Penn-Union to Metro to the Silver Line Express. That sounds like, even if all goes well, it would take forever and still require one to be up far too early. Reminds me of taking the train to get to 8am Saturday classes at Maryland. Nah.